This invention relates, generally, to a flange connection and more particularly to a flange connection having a lower profile and less weight through the use of a different seal and nut-bolt design.
In virtually every conduit or pipe installation where moderate to high pressures exist, a problem is always encountered as to flange design and usage. There are presently many flange structures on the market which are attached to conduit or the like by welding or compression type fittings. The relative size and complexity of these flanges varies with the size of the pipe and the pressure therein . Naturally, the larger the pipe and/or the pressure, the more expensive the flange connection. A typical 12" connection for 2500 psi will cost about $3,000-4,000.
An example, an extended industrial installation in the several thousand pound pressure range may easily have 60-70 flange connections. Obviously then, the cost of flange connections is a substantial factor in the overall cost of a project.
Further, flange connections have a tendency to be both heavy and bulky which further complicates installation.
Another problem with conventional flanges is the fact that they are subject to failure. This failure may be the result of seal failure, bolt failure or improper initial installation. It has been found that flange design lends itself to improper installation.
A typical prior art flange connection can be found, for example, in FIG. 1. Shown is a typical left and right half 10, 12 of a flange connection. The flanges have standard rims 20 which facilitate the use of a required number of conventional bolts 14 and conventional nuts 16. The flange faces 1 cooperate with the conventional therebetween. As is presently known, this type of arrangement, although quite common is quite problematic. More particularly, that portion of the flange face 1 adjacent the seal 22 must be relatively smooth or early seal failure will result. Further, the design itself requires that, for high pressure lines, a substantial number of bolts must be utilized, which must be torqued to a very high value in relation to the sealing pressure. Also, since buttress type threads for bolts and nuts are utilized, the bolts and nuts themselves must be of a substantial size.
By also referring to FIGS. 2A, 2B and 2C, there is illustrated prior art representations of conventional flange arrangements. Here, it can be readily seen how misalignment between the rims 20 due to uneven torquing of the bolts 14, results in skewing therebetween. Also evident is how this skewing causes conventional seals such as 22 to deform. As is obvious and readily known, improper seating of the seals 22 may cause early failure or leakage.
Referring to FIGS. 3, 4A and 4B, there is diagrammatically shown schematic and representational force and cross-sectional views of standard buttress type threads which are used in conventional flange connections. Due to the nature of buttress threads, one side of a thread is almost virtually perpendicular to the axis. As a result, nut threads closest to the support are stressed much more than the threads further away as is evident in FIG. 3. Therefore, the design of the flange connections must be based on stresses in the highest stressed first turn of the thread. This is one of the main reasons that substantial size bolts and nuts are used.
Yet however, buttress threads are standard for use in flange connections. The reason for buttress thread usage is that well over one hundred years ago, designers were concerned with the possibility of a nut freezing onto the bolt. They therefore favored a split nut design which allows the knocking off of the two halves of a nut even when the threaded joint was under load. As is readily known, a split type nut performs better when the thread reaction does not have a radial component which would produce a radial bursting force. Since the bearing surface of the buttress thread is substantially perpendicular to a bolt axis, it does not generate radial forces. Therefore, this type of thread was preferred by many designers. Today, however, proper coatings by all kinds of lubricants ensure smooth working of a nut without the danger of freezing. However, conventional design still prevails with the result that buttress threads are used even though other types of threads, such as truncated thread, are available.
Clearly, any solution which will lower the size, weight and cost of flange connections requires an improved seal and an improved nut and bolt design.